Thyroid Flashcards

1
Q

What is the name of an enlarged thyroid gland?

A

Goiter.

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2
Q

Describe the structure of the thyroid gland.

A

There are areas called colloid which are surrounded by simple cuboidal epithelial cells called follicular cells. The basolateral membrane is on the side outside of the colloid. The other membrane is the apical membrane.

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3
Q

What is the function of the thyroid gland?

A

Its main function is to synthesise and secrete Thyroid Hormone.

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4
Q

What precursor molecule is a major constituent of thyroid follicle?

A

Thyroglobulin.

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5
Q

What can be said about the blood supply in the thyroid gland?

A

It is very large and comes from both inferior and superior thyroid arteries.

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6
Q

What is the effect of the sympathetic nervous system on the thyroid gland?

A

This increases secretion of thyroid hormones.

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7
Q

What is the effect of TRH on the pituitary gland?

A

TRH binds to receptors and this increases calcium which causes exocytosis of TSH.

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8
Q

Where in the thyroid gland does TSH bind?

A

It binds to the basolateral membrane of the follicular cells.

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9
Q

Name three things which activation of a TSH receptor leads to.

A

Iodine uptake, production of Idothyrines, promotion of thyroid growth.

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10
Q

What does chronically high TSH lead to?

A

This stimulates thyroid growth and division of follicular cells leading to an enlarged gland.

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11
Q

Where is iodine for thyroid hormone synthesis derived from?

A

The diet.

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12
Q

What enzyme activates iodine so that it can combine with thyroglobulin?

A

Perioxidase enzyme.

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13
Q

Where is thyroglobulin produced?

A

This is produced by ribosomes in the follicular cells. It is then transported through the Golgi where it is glycosylated and packaged into vesicles before it is stored in the colloid.

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14
Q

What are thyroid hormones synthesised from?

A

Tyrosine residues on thyroglobulin.

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15
Q

What two substances do thyroid hormones bind to for transport in the blood?

A

Thyronine binding globulin (TBG) and also to albumin or pre albumin.

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16
Q

What is the effect of oestrogen in pregnancy on TBG?

A

Oestrogen increases synthesis of TBG which leads to less active T3 and T4 in circulation. Negative feedback allows these to increase and so overall there is more T3 T4 in circulation despite the fact that the same amount of the active form is present.

17
Q

What happens to T4 at peripheral tissues?

A

It undergoes deiodination which leads to T3. Thyroid hormones pass cell membranes, produce a response and are then broken down.

18
Q

Where are T3 and T4 deactivated?

A

In the liver and kidney due to removal of iodine.

19
Q

Why is T4 used to treat hypothyroidism?

A

This is more protected than T3 because it binds more tightly to TBG.

20
Q

What effects do thyroid hormones have on the body?

A

They increase the BMR by increasing mitochondria size and number which increases oxygen usage and heat production. There is also increased nutrient production. They also promote normal growth and tissue development.

21
Q

How do thyroid hormones affect the responsiveness of tissues?

A

Thyroid hormones make tissues more responsive to the sympathetic nervous system, and also other metabolic and reproductive hormones.

22
Q

Why do people with hypothyroidism have saggy skin?

A

Thyroid hormones stimulate turnover of proteins and glycoproteins in the skin.

23
Q

How does thyroid hormone affect the nervous system?

A

Thyroid hormone stimulates myelination of nerve fibres and neuron development. It also causes increase in reflex speed, and an increase in mental activity.

24
Q

What are the consequences of untreated hypothyroidism in newborns?

A

Mental retardation, delayed sexual development, coarse features and diminished linear growth.

25
Q

What are some of the symptoms of hyperthyroidism?

A

Heat intolerance leading to increased perspiration, weightloss, tachycardia (high pulse), increased bowel movements and appetite, nervousness and hyperreflexive (tremors)

26
Q

What is Graves’ disease?

A

This is an autoimmune disease where an antibody is produced which stimulates the TSH receptor on thyroid follicular cells.

27
Q

What is the action of carbimazole?

A

This inhibits incorporation of iodine with thyroglobulin. It thus reduces thyroid hormone levels.

28
Q

What are the treatment options for hyperthyroidism?

A

Radioactive iodine, carbimazole and surgical removal of thyroid gland.

29
Q

What is Hashimotos disease?

A

This is autoimmune destruction of thyroid follicles and production of an antibody which blocks TSH receptors on follicular cells.

30
Q

What is the treatment for hypothyroidism?

A

Oral T4. This is controlled until all symptoms of hypothyroidism disappear and there are no symptoms of hyperthyroidism.

31
Q

State some of the symptoms of hypothyroidism.

A

Fell cold, weight gain, low pulse, constipation, poor concentration, mood swings, dry skin, brittle nails and hair loss.

32
Q

What is the embryonic origin of the thyroid gland?

A

The thyroid gland is initially found positioned at the back of the tongue and rarely it can remain here. Usually it is under active due to poor vascular supply. Ovarian tumours can also be a source of thyroid tissue.

33
Q

In what condition can a goiter be present?

A

Hypothyroidism

34
Q

Where is the thyroid gland found?

A

The thyroid gland is a butterfly shaped gland in the neck.